1. Field of the Invention
This invention relates to pagers and is more particularly concerned with a miniaturized form of pager that can be fitted into a watch.
2. Prior Art
Pagers have long been known. They comprise a frame or coil constituting an antenna able to detect a coded magnetic field issued by a transmitter a relatively short distance away (a few dozen meters). If the received code corresponds to the code of the pager, stored in a memory, a transducer issues an acoustic signal and possibly an optical signal which warn the bearer of the pager that he must, e.g., dial a telephone number.
These paging devices are shaped like small boxes that can easily fit in a pocket. Besides the frame and the transducer, they comprise a number of electronic circuits and supply batteries.
The scope for a paging device increases when its size can be reduced, when it is able to detect a weak magnetic field, when it can issue a powerful acoustic signal, when its energy consumption is low and when it can be produced for low cost price.
To achieve maximum sensitivity of the frame to a sinusoidal magnetic field, the inductance of the frame is usually tuned to the frequency of the field by means of a capacitor. It is also known to connect an inductor in series with the transducer thereby to tune the latter to the frequency of the acoustic signal and hence to increase the power of the sound that is issued and to improve the efficiency of the transducer, the latter being the main user of energy in such a device.
These improvements are thus achieved by means of two components, a capacitor and an inductor, whose drawback, particularly the latter, is to take up a good deal of space in the device and to add to the cost of the latter. This is particularly bothersome when trying to reduce the size of the pager sufficiently to fit it in an electronic watch.
The idea of associating a pager with a watch is not new in itself. For example, Swiss Patent Specification No. 533332, or the corresponding German Patent Specification No. 2149535, mentions the possibility of including a pager in a watch but without however providing a form of embodiment. U.S. Pat. No. 3,937,004 describes a watch fitted with a pager that operates intermittently to save current. In this U.S. Patent specification, the means for picking up the external electromagnetic wave and the means for generating an acoustic signal are however not described in detail. Reference is merely made to an antenna and to a sound transmitter, but no details are given. Finally, Swiss Patent Specification No. 639816 describes an analogue watch wherein the coil of the motor is used between drive pulses as a detector able to detect interference magnetic fields. These fields may occur at various frequencies, thus making the tuning of the coil pointless.
In none of the above documents relating to the watch-making art is there any reference to a frame tuned by a capacitor and to a piezoelectric transducer tuned by an inductor nor is any reference made to the possibility of eliminating totally or partially the capacitor and the inductor whose drawback, as mentioned earlier, is to be space consuming and to be costly.